Soil organic carbon(SOC)in the forest ecosystem is the vital component of global carbon reservoir, and plays an important role in global carbon cycle and mitigation of global warming. Adopting field investigation and indoor analysis methods, the seven main forest types, i.e. Birch, Querous sclerophyllous, Cupressus funebris, Pinus yunnaniana, Cunninghamia lanceolat, Pinus massoniana and Pinus armandii were selected to investigate the variation of SOC densities and their controlling factors for the forest region of Guizhou Province, China. The main conclusions are drown as follows: (1)the average SOC density of Guizhou forest soil is 180.62Mg/hm~2, higher than soil carbon density (102.1Mg/hm~2) in forests of Jiangxi Province, indicating a high carbon sequestration in forest soils of Guizhou Province; (2)the SOC density ranges from 114.52Mg/hm~2 to 388.29Mg/hm~2, and significantly different between forest types (P<0.05) and decreases in the order of Pinus armandii>Cunninghamia lanceolat>Cupressus funebris>Querous sclerophyllous>Pinus massoniana>Birch>Pinus yunnaniana; (3)soil carbon density of forest declines with the increasing soil depth, and most of carbon was stored in the top soil (0-10cm); and (4)Pearson correlation analysis shows that there is no significant correlation between SOC density and slope, latitude as well as longitude.